Cadence入门（一）画出漏电流和源漏电压之间的关系：电路设计基础

写在前面的话：这篇讲Cadence的入门。请各位牛人们不要浪费时间看这篇了哈！

作者君意识到，相当多的读者是本科的小同学们。因此，作者君觉得不能只是一直讲具体的电路设计，还应该照顾到入门的同学们。

这一篇来自于作者君做TA时候的所用课件。（这是master的一个上机lab课程的课件，作者君做了三年TA。从Cadence的使用开始，一直到设计出一个完整的wide-band amplifier ，包括biasing电路 和最终的layout 。这门课还是很comprehensive的哈！话说两个星期的lab课程之后，大家纷纷表示以后要做analog designer……）

这位师兄的英文还挺好懂的，作者君就不一一翻译了，大家就当做四六级阅读了哈！不管怎么说，所有的IC design的EDA tools都是英文的，早些多接触一下英文并没有坏处。再说了，那些很经典的paper，基本上都是英文的。大家还是别抵触英文了哈！

学习模拟电路设计，作者君非常非常建议大家装个基本版的virtuso，不要什么6XXX那些高级版本，古老的5141就可以了。然后工艺库用多古老的都行。下面这个例子就是用的0.5um的工艺……老到……可能还有些做DCDC 的公司在用？反正只要device的model都还齐全就行了！

具体到不同的process，大家看到的有些界面可能会略微有些不同。但是别担心，基本上的流程就是这样的，只要能跑一个仿真，想必大家就会放心很多啦！

除此之外，大家还应该了解一些基本的Linux命令 ，因为基本上所有的EDA都是运行在Linux下面的。

Welcome to Analog Design Lab! I am pleased that you have chosen this course. I will be accompanying you for the next ten days. Let's embark on a fun & enriching journey ahead.

Exercise 1A: Plot of Drain Current with Drain-to-Source Voltage

1. Enter your User Name and Password and you will get the screen below:

2. Right click on the Mouse and Click Open Terminal. You will get the screen below:

4. Type source cshrc.amis05, press Enter and your screen will look like:

（这个source文件的功能是导入一些配置文件，比如环境变量之类的。其实如果IT的人给力的话，这一步其实是不用的）

5. Type icfb&, press Enter and your screen will look like:（icfb是较老版本的Cadence下面启动virtuoso 的命令，如果版本是6XX，就应该敲virtuoso &）

6. Click on Tools, and then Library Manager and your screen will look like:

7. Click on File, New and Library. Your screen will look like:

8. Under Name, type Analog_Is_Fun_Lab_Exercises, press Ok and your screen will look like:

9. Click Attach to an existing techfile, press OK. Make sure that the Technology Library is amis500cxakxx and the screen will look like shown below. Press OK.（链接工艺库。你的可能叫“smicXXX”，前面的字母一般就是foundry名）

10. You will get to see that you had created a new library - Analog_Is_Fun_Lab_Exercises:

11. Click on File, New and then Cell View. Your screen is shown:

12. Under Cell Name, type Lab_1a_NMOS . Your screen is shown:

13. Press OK. Your screen should show:

14. Now you are in the schematic window and ready to draw your schematic. Press i and an Add Instance window will pop up like shown below.

15. Click Browse. Select as shown below and a NMOS symbol will be attached to your mouse. Take note: enm is the name of a NMOS transistor.

16. Click on your left mouse once to place the NMOS symbol in the schematic window. Press Esc to remove the symbol from your mouse after placing it once in the window.

17. Press i again, click on Browse and choose as shown below. A DC voltage source will be attached to your mouse.

18. Click on your left mouse to place it in your schematic window. Move your mouse and left click again to place the second symbol. The final screen is shown below. Press Esc.

19. Press i again, click on Browse. In the AnalogLib, look for gnd symbol and place it in your schematic. It is a HAPPY test. Do try it yourself. I am sure you can do it. Your final screen should look like this below. Press [ to zoom out and ] to zoom in.

（键盘上的中括号键，就是字幕P旁边的两个，是放大和缩小的快捷键）

20. Excellent! You had finished the whole schematic. Now, let's continue with the wiring connections. Press w and left click once on the red square of the gnd symbol. Move the mouse towards the red square of the source of the NMOS symbol. Left click again. You can see that a wire connection is formed. Try the other wiring yourself. Do not be upset if you cannot do it. Ask your teaching assistant. He will be happy to assist you! Your finalized schematic will look like this. Press Shift and x together to save the schematic.

21. Now, we need to edit the properties (W/L ratio) of the NMOS. Press the Esc Button. Click on the NMOS symbol and it would be highlighted. Press q and then a window will pop up as shown below. Change the Finger width to 3 and the Length to 1.

Take note: 3 and 1 will be treated as 3um and 1um by the system respectively.

（一般的工艺下，后面都是带了单位的，比如um之类的。这个古老的工艺有些骨骼精奇……）

22. Now, we need to edit the properties (DC Value) of the voltage source(V0). Click on the V0 voltage source symbol and it would be highlighted. Press q and then a window will pop up as shown below. Change the DC voltage to 1.2. （设置bias的Vgs电压大小，必须保证比Vth大，否则下面的图可能看不到）

23. Do the same for V1 voltage source and change the value to 3. The final schematic should look like this. Press Shift and x together to save this schematic.

24. Now, we are ready for the simulation. Are you ready? Click on Tools, then Analog Environment. A new window will pop-up as shown below.

25. Click Setup, then Model Libraries. Under Model Library File, type this: /net/wildar/software2/local/library/AMIS/AMIS05_CDS/MSD_PDK/lib/amis500cx/tech/ spectre/amis500cxakxx/Rev2.20/res-Default.scs. Type typ under Section. After which, press Add. Your screen should look like this:（设置model的process corner，一般有typ，也就是typical，还有slow，fast，fs，就是fast-slow，和sf，一共五种。基于不同的process，可能还会有别的corner，名字也有可能不一样。如果你够幸运的话，这一步其实是不用手动加library的，可能已经被embedded进去了）

26. Repeat the same for the other 5 model files: cap, bip, dio, var and mos. It is a simple enjoyable test. Do try it yourself. Ask for help if you encounter any problems. Do not be shy. You will get the screen as shown below. Press OK. （你也有可能不用这样做，很多process默认加入了所有的device models）

27. In the Analog Design Environment window, press Setup, then Simulator, change the Project Directory to /tmp. It is shown below. Press OK.（告诉tool，你想把仿真结果保存在哪里。tmp是Linux下的临时文件夹，你也可以放在自己想放的任何地方，比如: /home/johnyy/simulation_results/nmos_test/）

28. In the Analog Design Environment window, press Analyses, then Choose. We want to run a DC simulation to sweep the drain to source voltage from 0V to 3V. Thus, it has to be filled up like the screen below. Press OK.（准备sweep那个mos的Vds值，设置了范围，用DC，也就是直流稳态仿真）

29. In the Analog Design Environment window, you should get the screen as shown:

30. In the Analog Design Environment window, press Outputs, To be plotted and Select on Schematic. Click on the red square at the bottom of V1 voltage source. After clicking on it, a green oval will surround the red square as shown below. This is so that the output result would be current. Overall, the graph plotted would be Id Vs Vds.（你也可以点击Results，然后direct plot，然后选择DC，再在schematic里面点击你想看的电压线或是电流节点）

31. In the Analog Design Environment window, it should be as shown below. Click on the Netlist and Run button as shown by the arrow below:（为了避免每次都要在schematic里面选择，你可以按Outputs，然后下面有to be plot，一次选好，下次跑simulation，结束之后，waveform就会自己弹出来）

32. After 5 seconds, a graph of Id Vs Vds would appear and will look like the graph below. If you get it, Congratulations! If you cannot get it, please do not despair. You just have to work harder at it. Look at the bright side of life.

这张图就是Id和Vds的关系，跟Razavi第二章里面的那个图是一样的。

33. Now, we are going to get a family of curves by running a parametric simulation. It is to sweep the V0 voltage values and a family of curves will emerge. Click on V0 voltage source and press q. Change the DC voltage to parameter. Press OK. In the schematic window, press Shift and x together to save it. （说实话，parameter这种名字其实不直接，作者君建议叫Vds_set 之类的名字，简单直接。注意：名字里别用空格）

34. In the Analog Design Environment window, click Variables, then Edit. Key in the information shown below. The maximum value of V0 is 2V. Press Add and OK.

35. In the Analog Design Environment window, it should be as shown below.

36. In the Analog Design Environment window, click Tools, then Parametric Analyses. The pop-up window is shown below. Fill in the information as shown below. It sweeps V0 from 1V to 2V in a total of 6 steps.

37. In the Parametric Analyses window, click Analysis, then Start. The family of curves are shown below.

这一系列的图，每个代表了不同的Vgs下，Id和Vds之间的关系。很显然，Vgs越大，这个mos能够运输的电流也更大，符合大家的估计哈！

Congratulations! I am so proud of you. You had obtained the family of curves for drain current plotted with drain-to-source voltage. Look at the curves. They are GREAT!

Do remember that parametric simulation is a very important step in circuit simulation as it saves a lot of time and effort as compared to simulating each component parameter separately. Check with your teaching assistant if you still have any doubts or queries with regard to any of the simulation steps above. He is a very nice and helpful person. No worries.

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